1. Field of the Invention
The present invention relates to an iron-base sintered part having an excellent strength, a manufacturing method of the iron-base sintered part and an actuator.
2. Description of the Related Art
Patent Reference 1 discloses a manufacturing method of a sintered part, in which carbon of 0.6 to 0.9 wt % is added in a composite alloy iron base powder, including Ni, Cu, Mo, etc., the powder combined with zinc stearate as a forming lubricant is put into a molding die, a forming body having density of 7.0 to 7.2 g/cm3 is formed, the forming body is sintered at a temperature of 1250 to 1300° C. and then is cooled continuously, thereby generating a martensite-bainite mixed composition. Also, Patent Reference 2 discloses Fe-base alloy having superior abrasion resistance, which is formed by impregnating a carbide precipitated type Fe-base sintered alloy having 5 to 20% porosity with Pb or Pb alloy.
[Patent Reference 1] Japanese Laid-Open Patent Publication No. Hei 5-78712
[Patent Reference 2] Japanese Laid-Open Patent Publication No. Hei 7-90513
The alloy disclosed in the above Patent Reference 1 relates to a method for generating a martensite-bainite mixed composition through continuous cooling, which does not include a carburization quenching process of rapid cooling after carburization. The density of 7.0 to 7.2 g/cm3 is likely high for sintered metal, however it is not always considered high density. This is assumed from the method of charging a metal powder into a cavity of a molding die at a normal temperature or the process of using zinc stearate as a forming lubricant in the technique disclosed in Patent Reference 1. Further, in the process of generating the martensite-bainite mixed composition, residual austenite, which is effective for securing toughness, is not generated. It is also described in paragraph No. 0017 in Patent Reference 1 that residual austenite is not generated. Also, the alloy disclosed in Patent Reference 2 is not subjected to a carburization quenching process.
Recently, a demand for higher performance with respect to an actuator is being increased more and more. Also with respect to an oil pump of a representative example of the actuator, a demand for higher pressure is being recently increased more and more. Because a rotor or a cam ring, which is used in the oil pump, is formed in an iron-base sintered part, strength, toughness and abrasion resistance are secured. However, a demand for higher performance and longer lifespan with respect to the iron-base sintered part is being recently increased more and more.